Blood sample collection and PRP production From all the patients who participated in the clinical trial, 27 ml of blood sample was collected with a 20-G needle from an antecubital vein so that the ratio of the blood and the anti-coagulant became 10:1. The collected blood samples were transferred to a prepared separation kit (Prosys PRP, Seoul, Korea) and underwent centrifugation at the speed of 3,000 RPM for three minutes. The buffy coat layer and the plasma of the upper portion of the layer were obtained and were transferred to a concentration kit (Prosys PRP, Seoul, Korea) using a 10-ml syringe. They again underwent centrifugation at the speed of 3,300 RPM for three minutes in order to obtain concentrated PRP.